Spatially-resolved analyses of aerodynamic fallout from a uranium-fueled nuclear test

Five silicate fallout glass spherules produced in a uranium-fueled, near-surface nuclear test were characterized by secondary ion mass spectrometry, electron probe microanalysis, autoradiography, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Several samples display compositional heterogeneity suggestive of incomplete mixing between major elements and natural U (U-238/U-235 = 0.00725) and enriched U. Samples exhibit extreme spatial heterogeneity in U isotopic composition with 0.02 < U-235/U-238 < 11.84 among all five spherules and 0.02 < U-235/U-238 < 7.41 within a single spherule. In two spherules, the U-235/U-238 ratio is correlated with changes in major element composition, suggesting the agglomeration of chemically and isotopically distinct molten precursors. Two samples are nearly homogenous with respect to major element and uranium isotopic composition, suggesting extensive mixing possibly due to experiencing higher temperatures or residing longer in the fireball. Linear correlations between U-234/U-238, U-235/U-238, and U-236/U-238 ratios are consistent with a twocomponent mixing model, which is used to illustrate the extent of mixing between natural and enriched U end members. (C) 2015 Elsevier Ltd. All rights reserved.